1. Field of the Invention
The present invention relates to a suspension controller for use in a vehicle, for example, an automobile.
2. Description of the Prior Art
Suspension controllers have heretofore been employed to effect attitude control of an automobile so as to improve steering stability or other running performance characteristics. One example of the suspension controllers is disclosed in Japanese Patent Application No. 01-67942 (1989). In this prior art, as shown schematically in FIGS. 1 and 2, transverse acceleration that acts on a vehicle body 2 is detected with a transverse acceleration sensor 1, and the detected transverse acceleration data is supplied to summing-up points 7 in a control means 6, where it is added to or subtracted from vehicle level data (detected with level sensors 4 respectively associated with four wheels 3, and pressure data (detected with pressure sensors 5) to calculate flow data for each wheel 3. Then, current data is calculated in a converter circuit 8 on the basis of each flow data. The current data thus obtained is output to a control valve 11 that is interposed between a cylinder 9 and a pump 10, which are associated with each of the four wheels 3, to control a pressure fluid supplied to each cylinder 9. In this way, the pressure balance among the cylinders 9 is changed to adjust the load distribution to the wheels 3, thereby suppressing the change in attitude of the vehicle, and thus improving the running performance.
In vehicles, excellent vehicle turning characteristics are particularly required in the early stage of a steering operation. To meet such requirements, the above-described conventional suspension controller is designed so that a travelling load that is shared by the cylinders on the rear wheel side is made higher than that on the front wheel side, for example, by making the gain by which the transverse acceleration data input to a proportional flow control valve on the rear wheel side is multiplied larger than the gain by which the transverse acceleration data input to a proportional flow control valve on the front wheel side is multiplied, thus obtaining excellent vehicle turning characteristics. In this case, however, over-steering may be induced, which is likely to be dangerous, and convergence (stability) deteriorates. If the load that is shared by the cylinders on the front wheel side is made higher than that on the rear wheel side, convergence is improved, but under-steering results, and the vehicle turning characteristics deteriorate.